1. Field of the Invention
This invention relates generally to telecommunication systems and assemblies, and more particularly to an acousto-optic bandpass filter.
2. Description of the Related Art
An important function in the telecommunication industry is signal switching. The switching can be performed either electronically or optically. In past years, the switching was accomplished through electronic means. However, with the increasing demand for lower cost, higher switching speeds, lower power consumption, and lower optical losses, optical switching is becoming more commonplace. There are two types of optical switches currently used; wavelength insensitive optical switches, and wavelength sensitive optical switches. The wavelength insensitive optical switches are typically broadband fiber-to-fiber switches used to redirect all the traffic from one optical fiber to another. Because the switching process is either thermo, electro-optic, or mechanical, the switching speed is satisfactory. However these switches do not satisfy the requirement of low cost, reliability, and low optical insertion loss.
The wavelength sensitive optical switches are needed for wavelength division multiplexed (WDM) signals because the wavelength separation between channels is small. A narrow optical band of traffic carried by a specific wavelength of a multi-wavelength signal may need to be separated from the rest of the traffic. A wavelength-sensitive optical switch can perform this function optically at considerable cost savings. Existing wavelength sensitive optical switches are usually bulky, have high power consumption, and high optical insertion losses. For instance, in a previous patent Tunable Optic Fiber Bandpass Filter Using Flexural Acoustic Waves, U.S. Pat. No. 6,151,427, by this inventor, I discuss an acousto-optic bandpass filter, however that invention uses a core block that introduces significant optical insertion losses, added complexity, and is costly to manufacture. The present invention does not require a core block component, thereby negating these problems and simplifying the architecture. Other acousto-optic filters include xe2x80x9cAcousto-optic Filter,xe2x80x9d U.S. Pat. No. 6,233,379 by Kim et al. hereby incorporated by reference. This invention performs the function of a band-stop filter and can select a limited number of optical bands (channels) simultaneously but does so at the cost of increased power consumption for each band selected to the limit of the acousto-optic generator. The current invention eliminates all the optical bands (channels) simultaneously without using any power and can select one or more channels to pass through the filter, thus performing a bandpass operation.
In consideration of the problems detailed above and the discrepancies enumerated in the partial solutions thereto, an object of the present invention is to provide an improved acousto-optic bandpass filter that does not require a coreblock and uses less electrical power.
Another object of the present invention is to provide a tunable acousto-optic filter.
Still another object of the present invention is to provide an acousto-optic bandpass filter with multiple acoustic signals that have individual controllable strengths and frequencies.
Yet another object of the present invention is to provide a broadband cladding mode coupler to efficiently couple all the optical traffic from the core mode to a cladding mode for later selection of individual optical channels.
Yet a further object of the present invention is to provide an acousto-optic bandpass filter that includes an optical fiber with a core and a cladding where the strength or the magnitude of an optical signal coupled from the cladding to the core is changed by varying the amplitude of radio frequency (RF) signal(s) applied to the acoustic wave generator.
In order to attain the objectives described above, according to an aspect of the present invention, there is provided an Acousto-Optic Bandpass Filter that includes a standard single-mode optical fiber with a core and a cladding surrounding the core in a concentric fashion. The optical fiber can support multiple cladding modes and a single core mode that is guided along the core. An acoustic wave amplifier has a base and a tip that is coupled to the fiber. The acoustic wave amplifier propagates an acoustic wave from the base to the tip and launches a flexural wave into the optical fiber. At least one acoustic wave generator is coupled to the base of the acoustic wave amplifier.
The acousto-optic bandpass filter is a device whereby one or more bands of optical wavelengths may be selected for further transmission. In this device, all light within the optical bandwidth of operation is first coupled from the core mode of a optical fiber to a specific cladding mode by a long period, typically photo or UV induced grating. These cladding mode lightwaves then enter an acousto-optic interaction region where selected RF frequencies of flexure waves, induced by acoustic wave generator, re-couple selected bands of wavelengths back into the core mode. The interaction region is isolated from the broadband coupler by an acoustic absorber to limit acoustic interaction to the interaction region.
In another embodiment of the present invention, an acoustic absorber is positioned between the broadband cladding mode coupler and the acoustic wave amplifier to prevent the acoustic waves from interfering with the broadband cladding mode coupler.
The aforementioned features, objects, and advantages of this method over the prior art will become apparent to those skilled in the art from the following detailed description and accompanying drawings.